Authors / CoAuthors
Exon, N.F. | Hill, P.J.
Abstract
The 50 000 km? East Tasman Plateau (ETP) is a roughly circular continental block, about 200 km across, that lies in water depths of 2200-2800 m. A variety of continental rocks including gneissic granite have been dredged from the plateau?s margins. The plateau is like a giant saucer, with basement rocks around the margin and sediments filling the central depression. The plateau supports Cascade Seamount, a late Eocene guyot that is probably related to the trace of the Balleny mantle plume. Seismic profiles suggest that the central plateau subsided under the weight of the guyot. Geophysical and petrological evidence suggest that the plateau was adjacent to the South Tasman Rise and the Tasmanian block until it was transported about 130 km east-northeast (relative to Tasmania) during early formation of the Tasman Basin in the Late Cretaceous (95-83 Ma), as part of the breakup of East Gondwana. Stretching and seafloor spreading formed the L?Atalante Depression between the plateau and the rise, and the East Tasman Saddle between the plateau and the Tasmanian block. Lord Howe Rise to the east separated from the East Tasman Plateau at ~83 Ma, as part of Tasman Basin spreading. The drilling of continuously cored ODP Site 1172 in 2000 has greatly improved our understanding of the ETP, giving us control down to the Late Cretaceous. The site was in 2620 m water depth and about 40 km west of the summit of Cascade seamount. Total depth was 766 m. Seismic profiles show that more than 3000 m of strata are preserved above basement in the central plateau, and most are probably of Cretaceous age. Our interpretations suggest that this area deep within Gondwana was blanketed by Late Cretaceous clastic sediments before there was a burst of volcanism at ~85 Ma during early rifting, followed by further clastic sedimentation and the documented onset of marine sedimentation. Site 1172 evidences the latest Cretaceous and younger history of the plateau. The sea was very shallow initially, but deepened slowly during Maastrichtian to middle Eocene times, more rapidly to outer shelf depths in the late Eocene, and very rapidly to bathyal depths in the Oligocene. Detrital input completely dominated the older sediments, and pelagic carbonate rain dominated the Oligocene and younger ones. The change is related to the final opening of the Tasmanian Gateway as Australia moved northward away from Antarctica, but mechanisms are still being assessed. Palynomorphs and diatoms characterise the detrital sediments, but nannofossils and planktonic forams the carbonates. The fossils show that the region was warm to temperate through the Maastrichtian to Eocene, and then cooled as climate gradually deteriorated. Site 1172 contains about 70 m of Maastrichtian marine and paralic mudstone, 315 m of early Paleocene to middle Eocene shallow marine mudstone, 20 m of late Eocene glauconitic shallow marine and condensed siltstone and sandstone, and 360 m of Oligocene and younger pelagic carbonates. Sedimentation rates were ~1.5 cm/ka in the Maastrichtian to middle Eocene, and generally very low thereafter. Major hiatuses occur in the mid Paleocene, early Oligocene and late Miocene.
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nonGeographicDataset
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42777
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- External Publication
- ( Theme )
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- marine
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- AU-TAS
- Australian and New Zealand Standard Research Classification (ANZSRC)
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- Earth Sciences
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- Published_Internal
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2003-01-01T00:00:00
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